Generally, human, particularly female, desire to keep skin white. Main detestable skin troubles are stain (chloasma) which increase with ageing and freckle which is more frequently observed in children, and various efforts have been made for preventing and treating these diseases. For such purposes, there have been employed a skin care with rice bran packed in a bag or mud, as well as a treatment of skin with sulfur, salicylic acid or enzymes which have an action peeling horny layers of skin, or vitamin C.
Both stains and freckles are a sort of dyschromia and a pigmentation which grows worse by ultraviolet. In these diseases, particularly in color of skin, melanin pigment participates, and hence, these diseases are usually treated by application of melanin-decomposing agents: bleaching agents (i.e., hydroquinone or derivatives thereof, mercury compounds or peroxides, etc.), by external or oral administration of adrenocortical hormone, or by administration of tyrosinase inhibitors.
However, since such bleaching agents and tyrosinase inhibitors damage original physiological functions of skin and induce undesirable side effects such as leukoderma, dyschromia, contact dermatitis, anemia or hyperthermia, they are not satisfactory. Thus, there is no positively effective method for the treatment of these diseases, but there is rather a passive method employed, such as avoiding sunshine or camouflaging with cosmetics.